For automatically painting vehicle bodies, for example, and other types of workpieces it is common to sequentially convey the vehicle bodies past one or more paint spray stations where the sides and the top of the vehicle body are coated. Each side of the vehicle body may be coated by one or more spray guns which are mounted on a reciprocator. As the body is conveyed in a horizontal direction past the spray guns, the reciprocator continuously moves the spray guns up and down and the spray guns are turned on to apply paint to the sides. One or more spray guns also are mounted on a top coater which reciprocates the spray guns horizontally in a transverse direction to sweep back and forth across the top of the vehicle body as the body is conveyed through the spray station for applying paint to the top.
Prior art side and top coaters of this type can apply a high quality coating to the sides and top of a box shaped workpiece, such as a refrigerator having a rectangular housing. However, most vehicle bodies have curved surfaces. The curved surfaces cause the spacing between the spray guns and the body to change and cause the angle of the surface being coated relative to the spray gun to change as the body is conveyed past the spray guns. In most cases, it is preferable to have each spray gun spray in a direction substantially perpendicular to the surface being coated.
Contour following apparatus presently used in the automobile industry for spray painting passenger car bodies is mechanically designed to follow contours to a limited extent. The apparatus is constructed to follow a single contour which represents an average for all types of car bodies to be painted by the apparatus. Thus, the spray guns can only follow a contour which represents the average and cannot follow the precise contour of each different shape car body. When the actual contour of the car body deviates significantly from the average contour followed by the coating apparatus, there is a decrease in the quality of the applied coating.